Thermosensitive recording media which utilize reactions between electron-donating coloring compounds thereinafter, sometimes referred as “coloring agent” or “leuco dye”) and electron-accepting compounds (hereinafter, sometimes referred as “color developer”) have been well-known, and have been broadly utilized as output papers of facsimiles, word processors and scientific instrumentation apparatuses, with an advance of office automation, and nowadays in magnetic thermosensitive cards such as a pre-paid card and point card. From an environmental issue, these conventional recording media in practical use are under pressure to review their use and are required to be recycled, and to be used in less amount; however, recorded images cannot be erased, and thus cannot be used repeatedly. In addition, new information is written only to non-recorded portion, and therefore the total areas capable of being recorded are limited. Thus, under the current situation, the amount of information to be recorded is reduced or a new card is issued when area to be recorded is fully occupied. Against the backdrop of waste problem or problem of deforestation, development of reversible thermosensitive recording medium which is rewritable many times had been desired.
From theses demands, various kinds of reversible thermosensitive recording media have been disclosed. For example, Patent Literatures 1 and 2 disclose a reversible thermosensitive recording medium which is a kind of those using polymer, in which physical change, i.e., transparent and white opaque is utilized. Alternatively, there has been proposed a reversible thermosensitive recording medium which is a kind of those using a dye, in which chemical change is newly utilized Specifically, for example, gallic acid is used in combination with phloroglucinol as a color developer (see Patent Literature 3). Such compounds as phenolphthalein and thymolphtalein are used as a color developer (see Patent Literature 4). Homogeneous mixed solution composed of coloring agent, color developer, and carboxylic acid ester are contained in a recording layer (see Patent Literatures 5, 6, and 7). Ascorbic acid derivatives are used as a color developer (see Patent Literature 8). Salts of bis(hydroxyphenyl)acetic acid or gallic acid and higher aliphatic amine are used as a color developer (see Patent Literatures 9 and 10).
Further, Patent Literature 11 discloses a reversible thermosensitive coloring composition and thermosensitive recording medium. In the reversible thermosensitive coloring composition, an organic phosphorus compound, fatty carbonyl acid compound, or phenol compound each containing a long-chain aliphatic hydrocarbon group as a is developing agent is combined with a leuco dye as a coloring agent, thereby allowing coloring and erasing easily depending on the heating and cooling condition. The developed condition and erased condition can be stably maintained at normal temperature and in addition, developing and erasing can be repeated. And then, Patent Literatures 12 and 13 disclose use of a phenol compound containing a long-chain fatty hydrocarbon group which compound has a specific structure.
In the reversible thermosensitive recording medium where these materials are employed, however, there were such problems that the rate of erasing is slow and thus it takes much time to rewrite erasing is inadequate, or thermal stability of color images is low. Further, in recent years, demands for output with mobile devices have been increased. In these mobile devices, usable power supply depends on the capacity of a dry battery or rechargeable battery, and thus rewrite with low energy or in a short time is required.
Therefore, Patent Literature 14 discloses a reversible thermosensitive recording medium in which a specific phenol compound is used, thereby allowing high contrast between developed condition and erased condition, high-speed erasing, and excellent stability of coloring of an image part. In this reversible thermosensitive recording medium in which the phenol compound is used, color images can be erased by means of a heating member such as a hot stamp, heat roller, or ceramic heater. Therefore, the reversible thermosensitive recording medium is suitable for practical use.
However, many of the phenol compounds exemplified in the above-mentioned Patent Literature 14 have high melting point, which requires heating to high temperature when color developing and erasing and thus requires application of high energy. As a result, some problems arise. Specifically, since pulse is required to be applied for a long time during recording, writing speed is slow, and further high temperature causes large damage to the recording medium, inviting occurrence of blowing trace. In addition, the power supply of the recording apparatus becomes large, resulting in larger rewriting apparatus.
Further, as the phenol compound described in the above-mentioned Patent Literature 12, those having relatively low melting point also have been proposed; however, the reversible thermosensitive recording media in which these compounds were employed exhibits satisfactory coloring sensitivity, but the preservability of the images is not satisfactory and thus the reversible thermosensitive recording media had low practical use.
Patent Literature 1
Japanese Patent Application Laid-Open No. 63-107584
Patent Literature 2
Japanese Patent Application Laid-Open No. 04-78573
Patent Literature 3
Japanese Patent Application Laid-Open No. 60-193691
Patent Literature 4
Japanese Patent Application Laid-Open No 61-237684
Patent Literature 5
Japanese Patent Application Laid-Open No. 62-138556
Patent Literature 6
Japanese Patent Application Laid-Open No. 62-138568
Patent Literature 7
Japanese Patent Application Laid-Open No. 62-140881
Patent Literature 8
Japanese Patent Application Laid-Open No. 63-173684
Patent Literature 9
Japanese Patent Application Laid-Open No. 02-188293
Patent Literature 10
Japanese Patent Application Laid-Open No. 02-188294
Patent Literature 11
Japanese Patent Application Laid-Open No. 05-124360
Patent Literature 12
Japanese Patent Application Laid-Open No. 06-210954
Patent Literature 13
Japanese Patent Application Laid-Open No. 10-95175
Patent Literature 14
Japanese Patent Application Laid-Open No. 10-67177